[SDAG] Allow scalable vectors in SimplifyDemanded routines

[reames]

Summary

This is a continuation of the series of patches adding lane wise support for scalable vectors in various knownbit-esq routines.

The basic idea here is that we track a single lane for scalable vectors which corresponds to an unknown number of lanes at runtime. This is enough for us to perform lane wise reasoning on many arithmetic operations.

[reames]

rebase and ping

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

2705

Have you already audited SimplifyDemandedBitsForTargetNode for scalable vectors?

[reames]

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

2705

Nope, good catch.

[reames]

address reviewer comment and add conservative bailout for target nodes

[reames]

ping

[craig.topper]

LGTM

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

 
 bool TargetLowering::SimplifyDemandedBits(SDValue Op, const APInt &DemandedBits,
                                           KnownBits &Known,
                                           TargetLoweringOpt &TLO,
                                           unsigned Depth,
                                           bool AssumeSingleUse) const {
   EVT VT = Op.getValueType();
 
-  // TODO: We can probably do more work on calculating the known bits and
-  // simplifying the operations for scalable vectors, but for now we just
-  // bail out.
-  if (VT.isScalableVector()) {
-    // Pretend we don't know anything for now.
-    Known = KnownBits(DemandedBits.getBitWidth());
-    return false;
-  }
-
-  APInt DemandedElts = VT.isVector()
+  // Since the number of lanes in a scalable vector is unknown at compile time,
+  // we track one bit which is implicitly broadcast to all lanes.  This means
+  // that all lanes in a scalable vector are considered demanded.
+  APInt DemandedElts = VT.isFixedLengthVector()
                            ? APInt::getAllOnes(VT.getVectorNumElements())
                            : APInt(1, 1);
   return SimplifyDemandedBits(Op, DemandedBits, DemandedElts, Known, TLO, Depth,
                               AssumeSingleUse);
 }
 
 // TODO: Under what circumstances can we create nodes? Constant folding?
 SDValue TargetLowering::SimplifyMultipleUseDemandedBits(
     SDValue Op, const APInt &DemandedBits, const APInt &DemandedElts,
     SelectionDAG &DAG, unsigned Depth) const {
   EVT VT = Op.getValueType();
 
-  // Pretend we don't know anything about scalable vectors for now.
-  // TODO: We can probably do more work on simplifying the operations for
-  // scalable vectors, but for now we just bail out.
-  if (VT.isScalableVector())
-    return SDValue();
-
   // Limit search depth.
   if (Depth >= SelectionDAG::MaxRecursionDepth)
     return SDValue();
 
   // Ignore UNDEFs.
   if (Op.isUndef())
     return SDValue();
 
   // Not demanding any bits/elts from Op.
   if (DemandedBits == 0 || DemandedElts == 0)
     return DAG.getUNDEF(VT);
 
   bool IsLE = DAG.getDataLayout().isLittleEndian();
   unsigned NumElts = DemandedElts.getBitWidth();
   unsigned BitWidth = DemandedBits.getBitWidth();
   KnownBits LHSKnown, RHSKnown;
   switch (Op.getOpcode()) {
   case ISD::BITCAST: {
+    if (VT.isScalableVector())
+      return SDValue();
+
     SDValue Src = peekThroughBitcasts(Op.getOperand(0));
     EVT SrcVT = Src.getValueType();
     EVT DstVT = Op.getValueType();
     if (SrcVT == DstVT)
       return Src;
 
     unsigned NumSrcEltBits = SrcVT.getScalarSizeInBits();
     unsigned NumDstEltBits = DstVT.getScalarSizeInBits();
case ISD::SIGN_EXTEND_INREG: {
     unsigned NumSignBits = DAG.ComputeNumSignBits(Op0, DemandedElts, Depth + 1);
     if (NumSignBits >= (BitWidth - ExBits + 1))
       return Op0;
     break;
   }
   case ISD::ANY_EXTEND_VECTOR_INREG:
   case ISD::SIGN_EXTEND_VECTOR_INREG:
   case ISD::ZERO_EXTEND_VECTOR_INREG: {
+    if (VT.isScalableVector())
+      return SDValue();
+
     // If we only want the lowest element and none of extended bits, then we can
     // return the bitcasted source vector.
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     EVT DstVT = Op.getValueType();
     if (IsLE && DemandedElts == 1 &&
         DstVT.getSizeInBits() == SrcVT.getSizeInBits() &&
         DemandedBits.getActiveBits() <= SrcVT.getScalarSizeInBits()) {
       return DAG.getBitcast(DstVT, Src);
     }
     break;
   }
   case ISD::INSERT_VECTOR_ELT: {
+    if (VT.isScalableVector())
+      return SDValue();
+
     // If we don't demand the inserted element, return the base vector.
     SDValue Vec = Op.getOperand(0);
     auto *CIdx = dyn_cast<ConstantSDNode>(Op.getOperand(2));
     EVT VecVT = Vec.getValueType();
     if (CIdx && CIdx->getAPIntValue().ult(VecVT.getVectorNumElements()) &&
         !DemandedElts[CIdx->getZExtValue()])
       return Vec;
     break;
   }
   case ISD::INSERT_SUBVECTOR: {
+    if (VT.isScalableVector())
+      return SDValue();
+
     SDValue Vec = Op.getOperand(0);
     SDValue Sub = Op.getOperand(1);
     uint64_t Idx = Op.getConstantOperandVal(2);
     unsigned NumSubElts = Sub.getValueType().getVectorNumElements();
     APInt DemandedSubElts = DemandedElts.extractBits(NumSubElts, Idx);
     // If we don't demand the inserted subvector, return the base vector.
     if (DemandedSubElts == 0)
       return Vec;
     // If this simply widens the lowest subvector, see if we can do it earlier.
     // TODO: REMOVE ME - SimplifyMultipleUseDemandedBits shouldn't be creating
     // general nodes like this.
     if (Idx == 0 && Vec.isUndef()) {
       if (SDValue NewSub = SimplifyMultipleUseDemandedBits(
               Sub, DemandedBits, DemandedSubElts, DAG, Depth + 1))
         return DAG.getNode(Op.getOpcode(), SDLoc(Op), Op.getValueType(),
                            Op.getOperand(0), NewSub, Op.getOperand(2));
     }
     break;
   }
   case ISD::VECTOR_SHUFFLE: {
+    assert(!VT.isScalableVector());
     ArrayRef<int> ShuffleMask = cast<ShuffleVectorSDNode>(Op)->getMask();
 
     // If all the demanded elts are from one operand and are inline,
     // then we can use the operand directly.
     bool AllUndef = true, IdentityLHS = true, IdentityRHS = true;
     for (unsigned i = 0; i != NumElts; ++i) {
       int M = ShuffleMask[i];
       if (M < 0 || !DemandedElts[i])
         continue;
       AllUndef = false;
       IdentityLHS &= (M == (int)i);
       IdentityRHS &= ((M - NumElts) == i);
     }
 
     if (AllUndef)
       return DAG.getUNDEF(Op.getValueType());
     if (IdentityLHS)
       return Op.getOperand(0);
     if (IdentityRHS)
       return Op.getOperand(1);
     break;
   }
   default:
+    // TODO: Probably okay to remove after audit; here to reduce change size
+    // in initial enablement patch for scalable vectors
+    if (VT.isScalableVector())
+      return SDValue();
+
     if (Op.getOpcode() >= ISD::BUILTIN_OP_END)
       if (SDValue V = SimplifyMultipleUseDemandedBitsForTargetNode(
               Op, DemandedBits, DemandedElts, DAG, Depth))
         return V;
     break;
   }
   return SDValue();
 }
 
 SDValue TargetLowering::SimplifyMultipleUseDemandedBits(
     SDValue Op, const APInt &DemandedBits, SelectionDAG &DAG,
     unsigned Depth) const {
   EVT VT = Op.getValueType();
-
-  // Pretend we don't know anything about scalable vectors for now.
-  // TODO: We can probably do more work on simplifying the operations for
-  // scalable vectors, but for now we just bail out.
-  if (VT.isScalableVector())
-    return SDValue();
-
-  APInt DemandedElts = VT.isVector()
+  // Since the number of lanes in a scalable vector is unknown at compile time,
+  // we track one bit which is implicitly broadcast to all lanes.  This means
+  // that all lanes in a scalable vector are considered demanded.
+  APInt DemandedElts = VT.isFixedLengthVector()
                            ? APInt::getAllOnes(VT.getVectorNumElements())
                            : APInt(1, 1);
   return SimplifyMultipleUseDemandedBits(Op, DemandedBits, DemandedElts, DAG,
                                          Depth);
 }
 
 SDValue TargetLowering::SimplifyMultipleUseDemandedVectorElts(
     SDValue Op, const APInt &DemandedElts, SelectionDAG &DAG,
bool TargetLowering::SimplifyDemandedBits(
     unsigned Depth, bool AssumeSingleUse) const {
   unsigned BitWidth = OriginalDemandedBits.getBitWidth();
   assert(Op.getScalarValueSizeInBits() == BitWidth &&
          "Mask size mismatches value type size!");
 
   // Don't know anything.
   Known = KnownBits(BitWidth);
 
-  // TODO: We can probably do more work on calculating the known bits and
-  // simplifying the operations for scalable vectors, but for now we just
-  // bail out.
   EVT VT = Op.getValueType();
-  if (VT.isScalableVector())
-    return false;
-
   bool IsLE = TLO.DAG.getDataLayout().isLittleEndian();
   unsigned NumElts = OriginalDemandedElts.getBitWidth();
-  assert((!VT.isVector() || NumElts == VT.getVectorNumElements()) &&
+  assert((!VT.isFixedLengthVector() || NumElts == VT.getVectorNumElements()) &&
          "Unexpected vector size");
 
   APInt DemandedBits = OriginalDemandedBits;
   APInt DemandedElts = OriginalDemandedElts;
   SDLoc dl(Op);
   auto &DL = TLO.DAG.getDataLayout();
 
   // Undef operand.
bool TargetLowering::SimplifyDemandedBits(
   } else if (Depth >= SelectionDAG::MaxRecursionDepth) {
     // Limit search depth.
     return false;
   }
 
   KnownBits Known2;
   switch (Op.getOpcode()) {
   case ISD::SCALAR_TO_VECTOR: {
+    if (VT.isScalableVector())
+      return false;
     if (!DemandedElts[0])
       return TLO.CombineTo(Op, TLO.DAG.getUNDEF(VT));
 
     KnownBits SrcKnown;
     SDValue Src = Op.getOperand(0);
     unsigned SrcBitWidth = Src.getScalarValueSizeInBits();
     APInt SrcDemandedBits = DemandedBits.zext(SrcBitWidth);
     if (SimplifyDemandedBits(Src, SrcDemandedBits, SrcKnown, TLO, Depth + 1))
if (ISD::isZEXTLoad(Op.getNode()) && Op.getResNo() == 0) {
       EVT MemVT = LD->getMemoryVT();
       unsigned MemBits = MemVT.getScalarSizeInBits();
       Known.Zero.setBitsFrom(MemBits);
       return false; // Don't fall through, will infinitely loop.
     }
     break;
   }
   case ISD::INSERT_VECTOR_ELT: {
+    if (VT.isScalableVector())
+      return false;
     SDValue Vec = Op.getOperand(0);
     SDValue Scl = Op.getOperand(1);
     auto *CIdx = dyn_cast<ConstantSDNode>(Op.getOperand(2));
     EVT VecVT = Vec.getValueType();
 
     // If index isn't constant, assume we need all vector elements AND the
     // inserted element.
     APInt DemandedVecElts(DemandedElts);
if (SimplifyDemandedBits(Vec, DemandedBits, DemandedVecElts, KnownVec, TLO,
       return true;
 
     if (!!DemandedVecElts)
       Known = KnownBits::commonBits(Known, KnownVec);
 
     return false;
   }
   case ISD::INSERT_SUBVECTOR: {
+    if (VT.isScalableVector())
+      return false;
     // Demand any elements from the subvector and the remainder from the src its
     // inserted into.
     SDValue Src = Op.getOperand(0);
     SDValue Sub = Op.getOperand(1);
     uint64_t Idx = Op.getConstantOperandVal(2);
     unsigned NumSubElts = Sub.getValueType().getVectorNumElements();
     APInt DemandedSubElts = DemandedElts.extractBits(NumSubElts, Idx);
     APInt DemandedSrcElts = DemandedElts;
if (!DemandedBits.isAllOnes() || !DemandedSubElts.isAllOnes() ||
         SDValue NewOp = TLO.DAG.getNode(Op.getOpcode(), dl, VT, NewSrc, NewSub,
                                         Op.getOperand(2));
         return TLO.CombineTo(Op, NewOp);
       }
     }
     break;
   }
   case ISD::EXTRACT_SUBVECTOR: {
+    if (VT.isScalableVector())
+      return false;
     // Offset the demanded elts by the subvector index.
     SDValue Src = Op.getOperand(0);
     if (Src.getValueType().isScalableVector())
       break;
     uint64_t Idx = Op.getConstantOperandVal(1);
     unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
     APInt DemandedSrcElts = DemandedElts.zext(NumSrcElts).shl(Idx);
 
if (!DemandedBits.isAllOnes() || !DemandedSrcElts.isAllOnes()) {
         SDValue NewOp = TLO.DAG.getNode(Op.getOpcode(), dl, VT, DemandedSrc,
                                         Op.getOperand(1));
         return TLO.CombineTo(Op, NewOp);
       }
     }
     break;
   }
   case ISD::CONCAT_VECTORS: {
+    if (VT.isScalableVector())
+      return false;
     Known.Zero.setAllBits();
     Known.One.setAllBits();
     EVT SubVT = Op.getOperand(0).getValueType();
     unsigned NumSubVecs = Op.getNumOperands();
     unsigned NumSubElts = SubVT.getVectorNumElements();
     for (unsigned i = 0; i != NumSubVecs; ++i) {
       APInt DemandedSubElts =
           DemandedElts.extractBits(NumSubElts, i * NumSubElts);
       if (SimplifyDemandedBits(Op.getOperand(i), DemandedBits, DemandedSubElts,
                                Known2, TLO, Depth + 1))
         return true;
       // Known bits are shared by every demanded subvector element.
       if (!!DemandedSubElts)
         Known = KnownBits::commonBits(Known, Known2);
     }
     break;
   }
   case ISD::VECTOR_SHUFFLE: {
+    assert(!VT.isScalableVector());
     ArrayRef<int> ShuffleMask = cast<ShuffleVectorSDNode>(Op)->getMask();
 
     // Collect demanded elements from shuffle operands..
     APInt DemandedLHS, DemandedRHS;
     if (!getShuffleDemandedElts(NumElts, ShuffleMask, DemandedElts, DemandedLHS,
                                 DemandedRHS))
       break;
 
if (ConstantSDNode *RHSC = isConstOrConstSplat(Op1)) {
           LHSKnown.One == ~RHSC->getAPIntValue()) {
         SDValue Xor = TLO.DAG.getNode(ISD::XOR, dl, VT, Op0.getOperand(0), Op1);
         return TLO.CombineTo(Op, Xor);
       }
     }
 
     // AND(INSERT_SUBVECTOR(C,X,I),M) -> INSERT_SUBVECTOR(AND(C,M),X,I)
     // iff 'C' is Undef/Constant and AND(X,M) == X (for DemandedBits).
-    if (Op0.getOpcode() == ISD::INSERT_SUBVECTOR &&
+    if (Op0.getOpcode() == ISD::INSERT_SUBVECTOR && !VT.isScalableVector() &&
         (Op0.getOperand(0).isUndef() ||
          ISD::isBuildVectorOfConstantSDNodes(Op0.getOperand(0).getNode())) &&
         Op0->hasOneUse()) {
       unsigned NumSubElts =
           Op0.getOperand(1).getValueType().getVectorNumElements();
       unsigned SubIdx = Op0.getConstantOperandVal(2);
       APInt DemandedSub =
           APInt::getBitsSet(NumElts, SubIdx, SubIdx + NumSubElts);
if (SimplifyDemandedBits(Op.getOperand(0), MaskLo, KnownLo, TLO, Depth + 1))
       return true;
 
     if (SimplifyDemandedBits(Op.getOperand(1), MaskHi, KnownHi, TLO, Depth + 1))
       return true;
 
     Known = KnownHi.concat(KnownLo);
     break;
   }
-  case ISD::ZERO_EXTEND:
-  case ISD::ZERO_EXTEND_VECTOR_INREG: {
+  case ISD::ZERO_EXTEND_VECTOR_INREG:
+    if (VT.isScalableVector())
+      return false;
+    [[fallthrough]];
+  case ISD::ZERO_EXTEND: {
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     unsigned InBits = SrcVT.getScalarSizeInBits();
-    unsigned InElts = SrcVT.isVector() ? SrcVT.getVectorNumElements() : 1;
+    unsigned InElts = SrcVT.isFixedLengthVector() ? SrcVT.getVectorNumElements() : 1;
     bool IsVecInReg = Op.getOpcode() == ISD::ZERO_EXTEND_VECTOR_INREG;
 
     // If none of the top bits are demanded, convert this into an any_extend.
     if (DemandedBits.getActiveBits() <= InBits) {
       // If we only need the non-extended bits of the bottom element
       // then we can just bitcast to the result.
       if (IsLE && IsVecInReg && DemandedElts == 1 &&
           VT.getSizeInBits() == SrcVT.getSizeInBits())
case ISD::ZERO_EXTEND: {
     Known = Known.zext(BitWidth);
 
     // Attempt to avoid multi-use ops if we don't need anything from them.
     if (SDValue NewSrc = SimplifyMultipleUseDemandedBits(
             Src, InDemandedBits, InDemandedElts, TLO.DAG, Depth + 1))
       return TLO.CombineTo(Op, TLO.DAG.getNode(Op.getOpcode(), dl, VT, NewSrc));
     break;
   }
-  case ISD::SIGN_EXTEND:
-  case ISD::SIGN_EXTEND_VECTOR_INREG: {
+  case ISD::SIGN_EXTEND_VECTOR_INREG:
+    if (VT.isScalableVector())
+      return false;
+    [[fallthrough]];
+  case ISD::SIGN_EXTEND: {
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     unsigned InBits = SrcVT.getScalarSizeInBits();
-    unsigned InElts = SrcVT.isVector() ? SrcVT.getVectorNumElements() : 1;
+    unsigned InElts = SrcVT.isFixedLengthVector() ? SrcVT.getVectorNumElements() : 1;
     bool IsVecInReg = Op.getOpcode() == ISD::SIGN_EXTEND_VECTOR_INREG;
 
     // If none of the top bits are demanded, convert this into an any_extend.
     if (DemandedBits.getActiveBits() <= InBits) {
       // If we only need the non-extended bits of the bottom element
       // then we can just bitcast to the result.
       if (IsLE && IsVecInReg && DemandedElts == 1 &&
           VT.getSizeInBits() == SrcVT.getSizeInBits())
case ISD::SIGN_EXTEND: {
     }
 
     // Attempt to avoid multi-use ops if we don't need anything from them.
     if (SDValue NewSrc = SimplifyMultipleUseDemandedBits(
             Src, InDemandedBits, InDemandedElts, TLO.DAG, Depth + 1))
       return TLO.CombineTo(Op, TLO.DAG.getNode(Op.getOpcode(), dl, VT, NewSrc));
     break;
   }
-  case ISD::ANY_EXTEND:
-  case ISD::ANY_EXTEND_VECTOR_INREG: {
+  case ISD::ANY_EXTEND_VECTOR_INREG:
+    if (VT.isScalableVector())
+      return false;
+    [[fallthrough]];
+  case ISD::ANY_EXTEND: {
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     unsigned InBits = SrcVT.getScalarSizeInBits();
-    unsigned InElts = SrcVT.isVector() ? SrcVT.getVectorNumElements() : 1;
+    unsigned InElts = SrcVT.isFixedLengthVector() ? SrcVT.getVectorNumElements() : 1;
     bool IsVecInReg = Op.getOpcode() == ISD::ANY_EXTEND_VECTOR_INREG;
 
     // If we only need the bottom element then we can just bitcast.
     // TODO: Handle ANY_EXTEND?
     if (IsLE && IsVecInReg && DemandedElts == 1 &&
         VT.getSizeInBits() == SrcVT.getSizeInBits())
       return TLO.CombineTo(Op, TLO.DAG.getBitcast(VT, Src));
 
case ISD::EXTRACT_VECTOR_ELT: {
     }
 
     Known = Known2;
     if (BitWidth > EltBitWidth)
       Known = Known.anyext(BitWidth);
     break;
   }
   case ISD::BITCAST: {
+    if (VT.isScalableVector())
+      return false;
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     unsigned NumSrcEltBits = SrcVT.getScalarSizeInBits();
 
     // If this is an FP->Int bitcast and if the sign bit is the only
     // thing demanded, turn this into a FGETSIGN.
     if (!TLO.LegalOperations() && !VT.isVector() && !SrcVT.isVector() &&
         DemandedBits == APInt::getSignMask(Op.getValueSizeInBits()) &&
case ISD::SUB: {
     }
 
     [[fallthrough]];
   }
   default:
     // We also ask the target about intrinsics (which could be specific to it).
     if (Op.getOpcode() >= ISD::BUILTIN_OP_END ||
         Op.getOpcode() == ISD::INTRINSIC_WO_CHAIN) {
+      // TODO: Probably okay to remove after audit; here to reduce change size
+      // in initial enablement patch for scalable vectors
+      if (Op.getValueType().isScalableVector())
+        break;
       if (SimplifyDemandedBitsForTargetNode(Op, DemandedBits, DemandedElts,
                                             Known, TLO, Depth))
         return true;
       break;
     }
 
     // Just use computeKnownBits to compute output bits.
     Known = TLO.DAG.computeKnownBits(Op, DemandedElts, Depth);
     break;

 static APInt getKnownUndefForVectorBinop(SDValue BO, SelectionDAG &DAG,
                                          const APInt &UndefOp0,
                                          const APInt &UndefOp1) {
   EVT VT = BO.getValueType();
   assert(DAG.getTargetLoweringInfo().isBinOp(BO.getOpcode()) && VT.isVector() &&
          "Vector binop only");
 
   EVT EltVT = VT.getVectorElementType();
-  unsigned NumElts = VT.getVectorNumElements();
+  unsigned NumElts = VT.isFixedLengthVector() ? VT.getVectorNumElements() : 1;
   assert(UndefOp0.getBitWidth() == NumElts &&
          UndefOp1.getBitWidth() == NumElts && "Bad type for undef analysis");
 
   auto getUndefOrConstantElt = [&](SDValue V, unsigned Index,
                                    const APInt &UndefVals) {
     if (UndefVals[Index])
       return DAG.getUNDEF(EltVT);
 

llvm/test/CodeGen/AArch64/active_lane_mask.ll

; CHECK-NEXT:    ret
   ret <vscale x 8 x i1> %active.lane.mask
 }
 
 define <vscale x 4 x i1> @lane_mask_nxv4i1_i8(i8 %index, i8 %TC) {
 ; CHECK-LABEL: lane_mask_nxv4i1_i8:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    and w8, w0, #0xff
 ; CHECK-NEXT:    index z0.s, #0, #1
+; CHECK-NEXT:    and w9, w1, #0xff
 ; CHECK-NEXT:    and z0.s, z0.s, #0xff
 ; CHECK-NEXT:    ptrue p0.s
 ; CHECK-NEXT:    mov z1.s, w8
-; CHECK-NEXT:    and w8, w1, #0xff
 ; CHECK-NEXT:    add z0.s, z0.s, z1.s
+; CHECK-NEXT:    mov z1.s, w9
 ; CHECK-NEXT:    umin z0.s, z0.s, #255
-; CHECK-NEXT:    and z0.s, z0.s, #0xff
-; CHECK-NEXT:    mov z1.s, w8
 ; CHECK-NEXT:    cmphi p0.s, p0/z, z1.s, z0.s
 ; CHECK-NEXT:    ret
   %active.lane.mask = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i8(i8 %index, i8 %TC)
   ret <vscale x 4 x i1> %active.lane.mask
 }
 
 define <vscale x 2 x i1> @lane_mask_nxv2i1_i8(i8 %index, i8 %TC) {
 ; CHECK-LABEL: lane_mask_nxv2i1_i8:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    // kill: def $w0 killed $w0 def $x0
 ; CHECK-NEXT:    and x8, x0, #0xff
-; CHECK-NEXT:    index z0.d, #0, #1
 ; CHECK-NEXT:    // kill: def $w1 killed $w1 def $x1
 ; CHECK-NEXT:    and x9, x1, #0xff
-; CHECK-NEXT:    and z0.d, z0.d, #0xff
+; CHECK-NEXT:    index z0.d, #0, #1
 ; CHECK-NEXT:    ptrue p0.d
+; CHECK-NEXT:    and z0.d, z0.d, #0xff
 ; CHECK-NEXT:    mov z1.d, x8
+; CHECK-NEXT:    mov z2.d, x9
 ; CHECK-NEXT:    add z0.d, z0.d, z1.d
-; CHECK-NEXT:    mov z1.d, x9
 ; CHECK-NEXT:    umin z0.d, z0.d, #255
-; CHECK-NEXT:    and z0.d, z0.d, #0xff
-; CHECK-NEXT:    cmphi p0.d, p0/z, z1.d, z0.d
+; CHECK-NEXT:    cmphi p0.d, p0/z, z2.d, z0.d
 ; CHECK-NEXT:    ret
   %active.lane.mask = call <vscale x 2 x i1> @llvm.get.active.lane.mask.nxv2i1.i8(i8 %index, i8 %TC)
   ret <vscale x 2 x i1> %active.lane.mask
 }
 
 
 ; Illegal types
 

llvm/unittests/CodeGen/AArch64SelectionDAGTest.cpp

TEST_F(AArch64SelectionDAGTest, SimplifyDemandedBitsSVE) {
   SDValue Mask1V = DAG->getSplatVector(InVecVT, Loc, Mask1S);
   SDValue N0 = DAG->getNode(ISD::AND, Loc, InVecVT, Mask1V, UnknownOp);
 
   SDValue Mask2S = DAG->getConstant(0x55, Loc, Int8VT);
   SDValue Mask2V = DAG->getSplatVector(InVecVT, Loc, Mask2S);
 
   SDValue Op = DAG->getNode(ISD::AND, Loc, InVecVT, N0, Mask2V);
 
+  // N0 = ?000?0?0
+  // Mask2V = 01010101
+  //  =>
+  // Known.Zero = 00100000 (0xAA)
   KnownBits Known;
   APInt DemandedBits = APInt(8, 0xFF);
   TargetLowering::TargetLoweringOpt TLO(*DAG, false, false);
-  EXPECT_FALSE(TL.SimplifyDemandedBits(Op, DemandedBits, Known, TLO));
-  EXPECT_EQ(Known.Zero, APInt(8, 0));
+  EXPECT_TRUE(TL.SimplifyDemandedBits(Op, DemandedBits, Known, TLO));
+  EXPECT_EQ(Known.Zero, APInt(8, 0xAA));
 }
 
 // Piggy-backing on the AArch64 tests to verify SelectionDAG::computeKnownBits.
 TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_ADD) {
   SDLoc Loc;
   auto IntVT = EVT::getIntegerVT(Context, 8);
   auto UnknownOp = DAG->getRegister(0, IntVT);
   auto Mask = DAG->getConstant(0x8A, Loc, IntVT);